Cast aluminum insulator cap



1965 F. 5. R055 ETAL CAST ALUMINUM INSULATOR CAP Filed NOV. 18, 1963 mar a4 TEE-=1 5 I 22- 24 W a v. to

INVENTOR5 FRANK d. R0615 46 Tu "T %W f s-C'Anz from 10,000 to 15,000 volts.

United States Patent 3,217,095 CAST ALUMINUM INSULATOR CAP Frank S. Ross and Thomas Oliver Van Tuyl, Hazel Park,

Mich., assignors to American-International Aluminum Corporation, Hazel Park, Mich., a corporation of Florida Filed Nov. 18, 1963, Ser. No. 324,297 5 Claims. (Cl. 174-488) This invention relates to an insulator suspension cap and more particularly to a suspension cap that can be manufactured from an aluminum alloy.

It has been common to manufacture caps of the type in question as steel forgings, but it is desirable that these caps be manufactured from aluminum. There are a number of reasons for this. In the first place, aluminum is lighter so that the entire load to be carried is greatly minimized by the use of aluminum caps rather than steel. Furthermore, the corona effect is such that with aluminum, the amount of voltage that can be carried can be increased It has been a problem, how ever, to manufacture an insulator cap of suffioient strength from aluminum that it will support the loads required without taking an inordinate amount of metal so that the manufacture from aluminum is uneconomical.

It is an object of the present invention to provide an aluminum insulator suspension cap which has excellent strength characteristics for its weight and one which is a far superior substitution for the previously utilized steel forgings because of its improved electrical characteristics and its decreased weight.

It is a further object to provide an aluminum suspension cap which has critical angles and dimensions as required by the devices to be supported.

Other objects and features of the invention relating to details of design will be apparent in the following description and claims.

Drawings accompany the disclosure and the various views thereof may be briefly described as:

FIGURE 1, a sectional view showing an assembly of an insulator cap, ceramic insulator, and extension link.

FIGURE 2, a sectional view of an enlarged cap showing the details of the wall design.

FIGURE 3, a side elevation of a completed cap.

In the carrying of high voltage across country, it has been common to have high voltage towers spaced at proper distances in the line of transmission and to carry a number of different and separate lines on these towers. These lines are usually suspended at various points by connecting a plurality of insulators one below the other in tandem line. However, it is necessary to cap the ceramic insulators with metal in order to attach one to the other and also to attach to the high tension tower. The insulators are actually sufliciently fragile that they cannot be clamped directly so that they are suspended in bell-like caps by the use of a proper adhesive or cement. It is desirable that this be done in such a way that the forces on the ceramic insulators are primarily compressive forces. Since thousands of these bell caps are used to support insulators, it is important that they be as inexpensive as possible and as light as possible. However, it has not been expedient or successful to simply substitute aluminum for the forged bel-l caps without a change of design. One reason for this is that the bell cap would not have sufiicient strength when using the same dimensions as the previous steel caps. Also, since aluminum is a relatively expensive material, it has not been economical to simply use any particular design to obtain this strength since the strength must be balanced against the quantity of aluminum that is used. The insulator bells must be capable of carrying extremely heavy loads that vary from 14,000 to 25,000 pounds. It will be appreciated, of course, that the loads on these assemblies are not only due to dead weight but also due to wind forces.

It has been found that these bells may be molded in unitary, smooth-outline pieces from aluminum and a suitable alloy has been an alloy which contains by weight 7 percent (7%) silicon, .25 to .40 percent magnesium and .10 percent copper. This composition is to be maintained in a high state of purity. This alloy has a high strength per weight ratio with good electrical property. It should be subjected to What is generally known as T-6 standard aluminum heat treat which includes solution and artificial age to give highest physical properties. As previously indicated, with the use of aluminum, the electrical loads which can be carried by the high voltage lines can be in creased, for example, from 10,000 to 15,000 volts. Thus, the capacity of the lines can be greatly increased by changing the bell caps from forged steel to aluminum. However, the structure of the caps is changed as will be described to obtain proper strength and to improve to a great degree the corona effect.

More specifically, with reference to the drawings, one type of insulator of ceramic material is shown at 20 having a central neck portion 22 which extends up into an aluminum bell 24, this bell having a clevis top 26 with holes 28 to support the bell. The neck portion 22 is held Within the bell by a ceramic cement 30 which fills the space between the neck portion and the interior of the bell so that compressive forces are developed by a gravity load exerted outwardly on the sides of the bell.

Within the neck portion 22 is a central bore 32 which receives and supports an extension link 34 having tapered formations 36 at the top to anchor into a cement material 38. The link can be made of an aluminum casting and can join with a similar clevis bell 24 which is suspended downwardly so that a series of insulators are supported, one above the other, to separate a power line from the actual supporting member of the high voltage tower.

In FIGURE 2, a sectional view of the bell is shown. The interior top surface is relatively fiat and joined by a radius curve to an outwardly flaring, relatively straight side wall 44. The interior angles of the hell are pretty well established as standard, the long portion 44 of the interior side wall having approximately a 12 angle with the vertical axis as shown in FIGURE 2 and the short portion adjacent the lip 46 having a required angle of about 22 /2 to the vertical axis. These angles are established in order to create the proper relationship with the ceramic insulators which are inserted into and cemented within the supporting bells. Suitable rough surfaces 40 and 42 are provided to establish a bond with the cement (see FIGURE 1).

The outer surfaces of the hell have been found to be critical. For example, the angle of the major portion of the outer wall of the hell, it has been found, should be approximately 14 to 19. In the illustration shown in FIG- URE 2, this angle is 1630. The draft angle of the lower lip of the bell is 30 in FIGURE 2, but this can vary from 10 to 30, moving down to a lower range for heavier and larger size bells so that the lip portion increases in thickness with the larger bells. The bells have been made in actual practice in three different sizes to use with 10,- 000 volts, 15,000 volts and 20,000 volts. The dimensional changes in the size ranges above mentioned are as follows for the dimensions A, B, D and H shown on FIGURE 2:

With the construction above defined, it has been found that with a minimum amount of metal, a maxi-mum amount of strength is obtained so that the weight can be kept at a minimum. The suspension units and the cost of the material can, therefore, be kept at aminimurn. The units, however, are designed for maximum strength so that they will adequately support the loads which are required.

What we claim is:

' 1. A bell cap for high voltage line insulators which comprises:

(a) a unitary molded bell formed as an aluminum casting having means at the top to fasten to a suspension unit,

(b) a shell forming the body of said bell having a reentrant recess with a relatively long, outwardly flaring wall disposed at an angle of about 12 to the axis of the bell and a relatively short re-entrant wall flaring inwardly at an angle of 22 /2 to the axis,

(c) said shell having an outer surface with a relatively long, outwardly flaring wall disposed at an angle of about 14 to 19 to the axis of the bell and a relatively short inturned wall tapering at about to 30 to the axis of the bell.

2. A bell cap for high voltage line insulators which comprises:

(a) a unitary molded bell of an aluminum casting alloy comprising 7% silicon, .25 to .40% magnesium and 10% copper having means at the top to fasten to a suspension unit,

(b) a shell forming the body of said bell having a re entrant recess with a relatively long, outwardly flaring wall disposed at an angle of about 12 to the axis of the bell and a relatively short re-entrant wall flaring inwardly at an angle of 22 /2 to the axis,

(c) said shell having an outer surface with a relatively long, outwardly flaring wall disposed at an angle of about 14 to 19 to the axis of the bell and a relatively short inturned wall tapering at about 10 to 30 to the axis of the bell.

3. A bell cap for high voltage line insulators which comprises:

(a) a unitary molded bell of a high strength aluminum casting alloy having a relatively flat interior top wall connected by a radius curve to an outwardly flaring relatively straight side wall gradually increasing in thickness from a base dimension adjacent the top wall ranging from .140 to .175 inch, the outward flare of the inside of said wall being approximately 12 and the outward flare of the outside of said wall being approximately 14 to 19.

(b) said bell having an inturned lip at the bottom of said flaring wall having an interior angle of about 22 /2 and an exterior angle ranging around 10 to 30, the overall depth of the bell ranging between 1 %2" 2 4. A bell cap for high voltage line insulators which comprises:

(a) a unitary molded bell of an aluminum casting alloy compnising 7% silicon, .25 to .40% magnesium and .10% copper, having means at the top to fasten to a suspension unit,

(b) said bell having a relatively flat interior top wall connected by a radius curve to an outwardly flaring relatively straight side wall gradually increasing in thickness from a base dimension adjacent the top wall ranging from .140 to .175 inch, the outward flare of the inside of said wall being approximately '12 and the outward flare of the outside of said wall being approximately 14 to 19,

(c) said bell having an inturned lip at the bottom of said flaring wall having an interior angle of about 22 /z and an exterior angle ranging around 10 to 30.

5. A bell cap as defined in claim 4 in which the thick ness of said inturned lip ranges from .190 inch to .250 inch.

References Cited by the Examiner UNITED STATES PATENTS 1,712,900 5/29 Osborne l74161 2,072,201 3/37 Dibble 174182 2,082,566 6/37 Berndt 174-182 X OTHER REFERENCES Electrical World, A. B. Change Co. advertisement, vol. 154, No. 18, Oct. 31, 1960, pages 78-80.

JOHN F. BURNS, Primary Examiner.

LARAMIE E. ASKIN, Examiner. 

1. A BELL CAP FOR HIGH VOLTAGE LINE INSULATORS WHICH COMPRISES: (A) A UNITARY MOLDED BELL FORMED AS AN ALUMINUM CASTING HAVING MEANS AT THE TOP TO FASTEN TO A SUSPENSION UNIT, (B) A SHELL FORMING THE BODY OF SAID BELL HAVING A REENTRANT RECESS WITH A RELATIVELY LONG, OUTWARDLY FLARING WALL DISPOSED AT AN ANGLE OF ABOUT 12* TO THE AXIS OF THE BELL AND A RELATIVELY SHORT RE-ENTRANT WALL FLARING INWARDLY AT AN ANGLE OF 22 1/2* TO THE AXIS, (C) SAID SHELL HAVING AN OUTER SURFACE WITH A RELATIVELY LONG, OUTWARDLY FLARING WALL DISPOSED AT AN ANGLE OF ABOUT 14 TO 19* TO THE AXIS OF THE BELL AND A RELATIVELY SHORT INTURNED WALL TAPERING AT ABOUT 10 TO 30* TO THE AXIS OF THE BELL. 